1. Field of the Invention
The present invention relates to a lens driving apparatus for a disk player, and more particularly to a structure of a movable portion of the lens driving apparatus.
2. Description of the Related Art
A disk player reads information recorded on a disk using laser light to read/write a signal optically. The lens driving apparatus drives for such a disk player drives an objective lens while focus control and tracking control are executed in accordance with the driving signals supplied to driving coils consisting of a focus coil and tracking coil wound on a holder provided with the objective lens.
The lens driving apparatus generally has respective natural resonance frequencies in the focus control and tracking control. These natural frequencies depend on physical resonance formed by e.g. size or mass of the holder. When the lens driving apparatus is driven in the vicinity of the natural resonance frequencies, harmful oscillation is given to the objective lens. An existing lens driving apparatus has a frequency shown in FIG. 12. In FIG. 12, the abscissa denotes a frequency and the ordinate denotes a gain and a phase. The amplitude characteristic illustrated in dotted line in FIG. 12 provides a gain that decreases substantially linearly with an increase in the frequency except a resonance point in a lower frequency region. The phase characteristic illustrated in solid line is substantially constant until the vicinity of 10 KHz with an increase in the frequency.
However, at a further higher frequency, because of the natural resonance of the lens driving apparatus, the phase characteristic abruptly changes in the vicinity of the natural resonance frequency (e.g. 20 kHz) as shown in FIG. 12. When the phase lag reaches 180xc2x0, the control servo system becomes unstable.
Therefore, the lens driving apparatus is designed so that each higher mode resonance is out of each servo band in view of the natural resonance frequency of each control system. Namely, by designing the servo band necessary for actual servo control at an upper limit of e.g. 2 kHz-5 kHz, the control system is made unaffected by the phase shift in the vicinity of the natural resonance frequency.
In recent years, the disk player is operated at a high rotating speed of a disk that is twice or fourth times of the standard rotating speed of the disk. Therefore, there is necessity of the read or write of a signal at a high speed by the lens driving apparatus for the disk player.
The signal read/write at the high speed enlarges each of the servo bands for the respective control systems so that they must be extended to a higher frequency band. However, as described above, the presence of the natural resonance frequency in the vicinity of 20 kHz makes it difficult to assure the margin for the each servo band and higher mode resonance, and hence makes each servo control system unstable.
An object of the invention is to provide a lens driving apparatus for a disk player which can be operated at a natural resonance frequency shifted to a high frequency for high speed read/write.
In order to attain the above object, in accordance with an aspect of the invention, there is provide a lens driving apparatus for a disk player for movably supporting a holder with an objective lens and a driving coil, wherein the holder comprises an upper wall on which the objective lens is fixed; and a pair of side walls which are integral to the upper wall and aligned apart from each other in a direction of tracking, and the driving coil is wound on each of side edges of the pair of side walls of the holder.
In accordance with another aspect of the invention, there is provided a lens driving apparatus for a disk player for movably supporting a holder with an objective lens and a driving coil in directions of focusing and tracking, wherein the holder comprises an upper wall on which the objective lens is fixed; and a pair of side walls which are integral to the upper wall and aligned apart from each other in a direction of tracking, and the driving coil is a plate-like printed coil which generates driving force in the directions of focusing and tracking and has a coil surface in parallel to each of side edges of the pair of side walls of the holder in both directions of tracking and focusing.
In accordance with still another aspect of the invention, there is provided a lens driving apparatus for a disk player for movably supporting a holder with an objective lens and a driving coil in directions of focusing and tracking, wherein the holder comprises an upper wall on which the objective lens is fixed, a pair of side walls which are integral to the upper wall and aligned apart from each other in a direction of tracking, and a pair of arms aligned apart from each other in a direction of focusing and protruding from the holder in a direction of tracking; and the driving coil is composed of a focus coil wound on the pair of side walls and a tracking coil wound on the pair of arms.
In accordance with the invention, since the left/right side plates are removed from the holder constituting a movable portion, the weight and size of the holder are decreased. This permits the natural resonance frequency to be shifted to a high frequency and lens driving apparatus to make a stabilized operation at a high speed.
The holder can be reinforced by using a plate-like printed coil as the driving coil.
The above and other objects and features of the invention will be more apparent from the following description taken in conjunction with the accompanying drawings.